Composite metal article



@Cfk. 2, 1934. I H, CRITCHETT' 1,975,742

COMPOS ITE METAL ART ICLE Filed May 12, 1953 ATTORNEY Patented Oct. 2,1934 COMPOSITE METAL ARTICLE 7 James H. Critchett, Douglaston, N. Y.,assignor to Electro Metallurgical Company, a corporation of WestVirginia Application May 12, 1933, Serial No. 670,672

2 Claims.

The invention is a composite article comprising a ferrous metal bodyprovided with a corrosion resistant surface. More specifically thearticle of the invention comprises a ferrous metal body 5 portionconsisting for example of steel or cast iron, and a securely bondedsurface portion consisting of an alloy of chromium, iron, copper, andsilicon, the said surface portion being alloyed -with the body portionat the interface.

The invention is based at least in part on the discovery thatsubstantially homogeneous alloys of chromium, iron, carbon, copper, andsilicon, described in my application Serial Number 670,- 673 filed May12,1933, and containing about 4% 8% to 40% silicon, less than 6% carbon,and the remainder iron, are not only extremely resistant to corrosion,but also are adapted for use to form a coating securely bonded to thesurface of ferrous articles. I

The homogeneous alloys of chromium, iron, copper, and silicon, go intosolution with ferrous materials at moderately elevated temperatures withan unpredictable and surprising readiness that may not be simplyexplained by the fact that these alloys have a low melting point.

Especially useful as coating alloys are the compositions containing 20%'to 80% copper, 5% to 50% chromium, 1 5% to 40% silicon, and theremainder iron and carbon.

The composite article may be formed by known methods. For example, asand mold or chill mold may be coated with a paste formed fromgranulated coating alloy and a binder, as described for instance in U.S. Patent 1,588,111 to Charles B. Jacobs, and the base metal cast intothe coated mold. Or the ferrous metal article to be coated may be packedin granulated coating alloy mixed with a flux, and the article and alloyheated to of the article and coating alloy as described in U. S; Patent1,672,444 to Frederick M. Becket.-

These two methods are shown diagrammatically in Figures 1 and 2 of theaccompanying drawing, in which:

Figure 1 is a diagrammatic cross-section of a sandmold containing acomposite cast article,

Figure 2 is a diagrammatic"cross-section. of a and a cementationmixture, and

Figure 3 is a diagrammatic cross-section of a representative compositearticle.

In Figure 1, a sand mold consisting for example of an outer shell 13 anda sand inner surface 12, is coated with comminuted coating to 50%chromium, about 8% to 80% copper, about cementing temperatures below themelting points cementing box containing an article to be coated alloyand a binder 11. Into the coated mold, the body metal 10 is cast. If thebody metal 10 is cast iron, the above-described coating alloy forms acoating securely bonded by interalloying with the cast iron, but thereis little diffusion of the coating alloy into the base metal unless thelatter is cast very hot; if the body metal 10 is a steel, there is aconsiderable amount of diffusion of the coating alloy into the steel,the amount of such diffusion increasing as the casting temperature israised.

In Figure 2, an iron or steel article 20 is packed in a mixture ofcomminuted coating alloy and flux 21, in a metal box 22, and the boxthen heated to cementing temperatures. By the use of this method, afirmly bonded surface layer is obtained, and there is comparativelylittle diiiusion of the cementing alloy into the'main body of thearticle.

Figure 3 is a cross-section of the composite articles of the invention,showing a body metal 30 and a corrosion resistant surface portion 31.

In Figures 1, 2, and 3, the surface portion has been shown relativelythicker than will usually be desired for the sake of clarity. .80

I claim:

-" 1. A composite article comprising a ferro metal body portion and acorrosion resistant surface portion composed of a substantiallyhomogeneous alloy having a composition within the ,limits 4% to 50%chromium, 8% to 80% copper,

chromium, 15% to 40% silicon, carbon in an 1 amount not over*'5%, andthe remainder iron; said surface portion being tlrmlybonded to the bodyportion.

- JAMES H. CRITCHE'I'I.

